The present invention relates generally to prosthetic devices and, more particularly, to a valve assembly for use with a prosthetic limb socket.
A prosthesis is often used to replace an amputated portion of a limb and to help restore the amputee's ability to use that limb. A prosthesis for a lower extremity amputation will often include an artificial foot connected to an upright assembly (pylon, tube or shaft) which is in turn connected to a custom fitted socket assembly (it is also known in the art to use non-custom fitted socket assemblies). If the amputation is an above-the-knee amputation, the upright assembly will commonly include an artificial knee joint.
An above-the-knee prosthesis typically requires two interlaying sockets; an inner socket consisting of a flexible, thermoplastic material, and a stronger, less flexible, thermoplastic outer socket which is attached to the upright-assembly of the prosthesis. The inner socket is typically designed to interface with and cushion the amputee's residual limb, to protect the amputee's residual limb from the interconnection components which attach the socket assembly to the upright assembly, and to provide an air-tight seal between the residual limb and the outer socket.
This type of prosthesis is typically held on the patient by suction formed in the socket. Therefore, the inner socket will typically include a valve system positioned in the distal inner thigh portion of the socket assembly to release air trapped between the wearer's residual limb and the inner socket as the wearer is inserting the residual limb into the socket. After insertion of the residual limb in the socket, the valve system will be closed, thus forming the suction within the socket.
One typical valve system includes an annular valve housing permanently formed into a projection extending from the inner socket, and a valve which is usually threadedly engaged within a threaded hole in the annular valve housing. Such a valve system is typically constructed such that it protrudes from the inner socket through a hole in the outer socket to provide access to the valve system. Construction of the inner socket for this type of valve system typically includes the step of drape forming or blister forming a thermoplastic socket cone over a socket mold having the valve housing attached thereon. The valve housing will thus be vacuum formed or permanently laminated into the socket during fabrication of the socket. Excess plastic is then ground from around the valve housing to expose and facilitate access to the threaded hole in which the valve will engage. A valve can then be threadedly engaged into the valve housing such that gas may be transferred through the valve.
A disadvantage with such a fabricating process is that during the blister forming operation the plastic cone will catch on the fabrication plate and will periodically stretch thin in that area. Also, the transition from the inner surface of the socket to the valve can be very rough and uneven. Furthermore, because the valve housing is permanently molded into the socket, if there is a failure in the valve housing the entire inner socket may need to be re-fabricated.
Another typical valve system includes a valve housing comprised of two pieces. An annular housing member extending through the inner socket, having an annular flange for providing a seat and a seal against the inner surface of the socket; and an annular nut member which threadedly engages the outer circumference of the annular housing member extending from the inner socket. Once the nut member is threaded on the housing member, thus attaching the housing to the socket, a valve can then be threadedly engaged within the valve housing. Construction of the inner socket for this type of valve system will typically include the step of vacuum forming a thermoplastic preform cone over a positive cast of the amputee's residual limb having a definition-plate attached to the positive cast in the location of the vacuum housing. Once the socket is formed, a hole will be drilled into socket projection formed by the definition plate to facilitate insertion of the valve housing member.
A disadvantage with this type of valve system is that the thickness of the socket around the valve housing is unpredictable, and therefore, the fit of the valve housing within the socket will also be unpredictable.
An additional disadvantage with both valve systems described above is that, because of the inner thigh location of the valves, when the residual limb is inserted into the sockets the valve systems do not release air directly from the distal end (or bottom) of the sockets. The distal end of the limb may cover and seal off the valves in the sockets before the limb can be completely inserted into the sockets, preventing air from being released from the sockets. This may result in an undesirable air pocket between the distal limb and the distal end of the sockets.
Another disadvantage with the above valve systems is the requirement of the two sockets. Besides the added time and expense of creating an inner socket in the first place, if the inner socket needs to be re-fabricated due to damage or needs to be re-fitted due to a change in the limb dimensions, the hole on the outer socket for the valve may no longer align with the valve projection protruding from the inner socket. Furthermore, two sockets can give the prosthesis a long profile; thus if the amputation is immediately above the knee, the prosthesis may undesirably extend the thigh portion beyond where the knee joint should be.
Yet another disadvantage with the above valve systems is that the valve systems do not facilitate the forced suction of gas from, or the forced injection of gas into the socket. Oftentimes the volumetric dimensions of the residual limb will change within a very short period of time due to fluid retention or fluid loss. A volumetric loss can result in socket retention problems, which could be corrected using forced suction. A volumetric gain can result in the residual limb being mechanically locked into the socket; and removal of the socket in such an instance could be greatly assisted using forced air injection.
Accordingly, a need exists for an improved valve system which will reduce the amount of skill, time, and equipment needed to fabricate or replace a prosthesis. A need exists for a valve system which helps to reduce the levels of variance in the socket fabrication processes. A need exists for a valve system which facilitates easier donning of the prosthesis by reducing time and effort required by the amputee to attach the prosthetic limb to the residual limb. Furthermore, a need exist for a valve system which facilitates forced suction and forced injection of air from and into the socket.